WO-A-03/011378 discloses an injection device where a syringe is enclosed in a housing of barrel-like form, the syringe being propelled forward by a drive mechanism to project its needle, followed by continued operation of the drive mechanism to push the plunger of the syringe and eject a dose. This procedure will leave the needle sticking-out, unless certain measures are taken. One answer is to have an arrangement for withdrawing the syringe back into the housing, while another is to have a needle shroud that moves out from the housing to enclose the-needle. Of course, this must not interfere with the actual injection operation. It has therefore been proposed that the shroud is normally spring urged forwardly to a needle protecting position, but when the device is pushed against the patient's skin the shroud is forced to retract against its spring. After injection, the spring pushes the shroud forwards again. A mechanism is provided for automatically locking the shroud at its fully projecting position after the injection but not before. The device of WO-A-03/011378 comprises a housing for the syringe, a needle-shroud captive to the leading end of the housing and movable before use between extended and retracted positions, a drive member releasable from a rearward position within the housing to urge the syringe forwards to project its needle beyond the retracted needle shroud and then to express a dose through the needle, and locating members on the housing for capturing the drive member at its forward position attained after expressing the dose, and wherein the captured drive member is arranged to block retraction of the needle shroud from its extended position.
EP-A-1968670 discloses a substance delivery device (auto-injector) for use with a container (such as a syringe) containing the substance, the device comprising a body arranged to house or hold the container; a plunger which is movable with respect to at least a portion of the body, the plunger being arranged to act upon the container so as to move the container with respect to said portion of the body; wherein the plunger is also arranged to expel at least a portion of the substance from the container; and wherein the device comprises means for adjusting the amount of substance to be expelled from the container. The device can also have means for priming the container, and can accommodate containers of different size or shape.
FIG. 6 is a sectional view of an embodiment of the device disclosed in EP-A-1968670. The injection device 1 comprises a body or housing 2, which has three portions. These are (in the order from the proximal end of device 1 to the distal end): a main body 10, a mid-body 13 and a shroud retainer 15, the main body 10 is subdivided into a proximal main body portion 11 and a distal main body portion 12. These portions can be formed as one piece. The housing 2 carries or houses a sleeve-like syringe carrier 82, which is an example of a container carrier. The syringe carrier 82 in turn carries a syringe 20 (or other container for a substance). Syringe 20 comprises a generally cylindrical container portion 24 for accommodating a fluid 22, and a cannula 26. The needle is in communication with the interior of container portion 24 so that the fluid 22 may be expelled through cannula 26. A bung 28 is inserted in the container portion 24 at the proximal end. The bung 28 seals the fluid 22 within the container portion 24. Syringe 20 is biased towards the proximal end by means of spring 23. This spring 23 is however relatively weak. Cannula 26 is initially protected by a needle sheath 29.
A safety cap or needle sheath remover 30 is provided at the distal end of injection device 1. This safety cap 30 is carried by the shroud retainer 15 of housing 2. Towards its proximal end the safety cap 30 is hooked over the proximal end of needle sheath 29 so that, when safety cap 30 is removed, the needle sheath is removed as well.
The distal end of injection device 1 is also provided with a needle guard 32 or “lockout shroud”. This needle guard 32 is moveable along the longitudinal axis of the injection device over a limited range. The needle guard 32 is initially covered, and prevented from moving, by safety cap 30. Only once safety cap 30 has been removed (as will be explained below) can needle guard 32 move.
Towards the proximal end of injection device 1 there is provided a plunger 40, which has a distal portion 41 and a proximal portion 42. The plunger is biased by spring 50 towards the distal direction. This bias is relatively strong, and much stronger than the bias provided by spring 23.
At the very proximal end of injection device 1 there is provided a firing button assembly. Its structure and function will be explained below.
The core principle of operation and much of the structure of the injection device 1 is very similar to the technique disclosed in WO 03/011378. Essentially, as in that earlier document, after removal of the safety cap 30 (and needle sheath 29) the needle guard 32 extends in distal direction because of the bias provided by a spring 34. The distal end of the injection device 1 is then pressed against a patient's skin. This pushes needle guard 32 in proximal direction against the bias of spring 34. However, during this action the cannula 26 does not project beyond the distal end of needle guard 32.
As in the earlier-disclosed technique, when the firing button is depressed the plunger 40 is released and can move in distal direction. When the front surface 45 of plunger 40 contacts bung 28, continued movement of the plunger in distal direction initially moves syringe 20 (i.e. not just bung 28) in distal direction. This is so because the force required to move bung 28 in distal direction with respect to container portion 24 is greater than the force required to move the entire syringe 20 in distal direction (to this end the interior surface of the container portion 24 can be provided with circumferential ribs or other friction increasing formations). During this movement of syringe 20 the cannula 26 penetrates the skin of the patient. Eventually the movement in distal direction of syringe 20 comes to a halt, but plunger 40 is still able to move further in distal direction. This leads to bung 28 being moved in distal direction with respect to container portion 24, which means that fluid 22 is expelled from container portion 24 through cannula 26 into the patient. Hence the movement of the syringe 20 (as a whole) and the movement of bung 28 within syringe 20 is brought about by plunger 40 acting on bung 28. It will be appreciated that the portion of plunger 40 (i.e. distal end surface 45) which acts on the syringe 20 to move the syringe is the same as the portion of the plunger which acts on the syringe to move bung 28 so as to expel the fluid. When the plunger 40 has its movement in distal direction stopped the injection operation has been completed. The user can then move the injection device 1 in proximal direction so as to withdraw the needle from the injection site. As the injection device 1 is withdrawn from the skin of the patient the needle guard 32 is moved in distal direction due to the bias provided by spring 34. The guard 32 then locks in the distal position rendering the device safe. The injection device 1 can then be disposed of.
In contrast to the earlier-disclosed injection device, EP-A-1968670 discloses several additional features. Most notably these additional features are an adjustment means for adjusting the dose to be injected, and a priming function.
The adjustment means of EP-A-1968670 primarily comprises a stop member 44 carried by the distal plunger portion 41. Stop member 44 may be provided with an internal thread co-operating with an external thread 43 on the circumferential surface of the distal plunger portion 41. Additionally, stop member 44 is keyed at 46 to the inner surface of distal housing portion 12. With stop member 44 being threadibly engaged with the distal plunger portion 41 and being keyed to distal housing portion 12 (e.g. by means of splines or similar, not shown), the stop member 44 will move in distal or proximal direction when distal plunger portion 41 is rotated about its longitudinal axis.
Distal plunger portion 41 can be rotated by means of adjustment ring 48. Adjustment ring 48 is keyed to a relatively large diameter proximal portion 49 of the plunger 40. This means that, on rotation of adjustment ring 48, the distal plunger portion 41 will carry out the same rotation, but the distal plunger portion 41 is substantially free to move in a direction parallel to the plunger axis, independently from adjustment ring 48. The proximal portion 49 of the distal plunger portion 41 is engaged with the distal portion 47 of the proximal plunger portion 42 such that the distal plunger portion 41 can substantially freely rotate with respect to the proximal plunger portion 42 but has to make the same movements in distal or proximal direction as the proximal plunger portion 42.
The adjustment ring 48 is located between proximal and distal main body portions 11 and 12. Windows 14 are provided on opposite sides of main body 10 where the proximal and distal main body portions 11 and 12 meet.
The injection device 1 has a generally oval cross section. The windows 14 are provided on those “sides” of the oval which have the smaller distance from the centre of the oval. The main body is continuous on those “sides” of the oval which have the greatest distance from the centre of the oval. This means that the main body 10 with proximal and distal main body portions 11 and 12 can be formed (e.g. moulded) in one piece and further that adjustment ring 48 can project through windows 14 whilst being securely held within main body 10.
In order to adjust the dose to be injected the user can rotate adjustment ring 48, thereby rotating the plunger 40. As mentioned, this sets the axial position of stop member 44 along distal plunger portion 41. Through setting this axial position the user can determine how far the plunger is allowed to project into container portion 24. This is so because movement of the plunger in distal direction during the injection process is stopped when stop member 44 makes contact with the proximal end of container portion 24. The axial position of stop member 44 along distal plunger portion 41 (before the beginning of the injection operation) can be viewed by the user through a further window 16 provided in the distal main body portion 12. Suitable indications may be provided at window 16 to indicate to the user which dose corresponds to the set position of stop member 44 with respect to window 16.
EP-A-2633874 discloses a medicament delivery device comprising a housing, a safety sleeve movable between an extended position and a retracted position relative to the housing, a guide sleeve rotatably disposed in the housing, a plunger slidably disposed in the safety sleeve, and a button coupled to the housing. When the safety sleeve is in the retracted position, translation of the button relative to the housing causes the guide sleeve to rotate relative to the safety sleeve. Rotation of the guide sleeve relative to the safety sleeve allows the plunger to translate a predetermined axial distance relative to the safety sleeve.